How to Download Files from the Web Using Python 3?

Downloading Files from the Web in Python 3

When extracting URLs from JAD files for downloading JAR files, we encounter an error due to the URL being stored as a string type. To resolve this issue, we explore methods to download files with string URLs in Python 3.

Retrieving Web Page Contents:

To fetch the contents of a web page into a variable, we can use urllib.request.urlopen and read the response:

<code class="python">import urllib.request

url = 'http://example.com/'
response = urllib.request.urlopen(url)
data = response.read()      # bytes object
text = data.decode('utf-8') # str object</code>

Downloading and Saving Files:

For straightforward file downloads and saving, urllib.request.urlretrieve is optimal:

<code class="python">import urllib.request

# Download and save file from url to file_name
urllib.request.urlretrieve(url, file_name)</code>

Alternatively, you can obtain the local path and response headers:

<code class="python">file_name, headers = urllib.request.urlretrieve(url)</code>

Optimal Solution Using urlopen and shutil.copyfileobj:

The recommended approach is to utilize urllib.request.urlopen to retrieve a file-like HTTP response object and copy it to a file using shutil.copyfileobj:

<code class="python">import urllib.request
import shutil

# Download and save file from url to file_name
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
    shutil.copyfileobj(response, out_file)</code>

Alternative Approach for Small Files:

For smaller files, it's possible to store the entire download in a bytes object and write it to a file:

<code class="python">import urllib.request

# Download and save file from url to file_name
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
    data = response.read() # bytes object
    out_file.write(data)</code>

Extracting Compressed Data on the Fly:

You can also extract compressed data on the fly if the HTTP server supports random file access:

<code class="python">import urllib.request
import gzip

# Read first 64 bytes of .gz file at url
url = 'http://example.com/something.gz'
with urllib.request.urlopen(url) as response:
    with gzip.GzipFile(fileobj=response) as uncompressed:
        file_header = uncompressed.read(64) # bytes object</code>

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